Is weight gain an issue? Is she having enough wet and poopy diapers? If she's gaining and having enough output, I personally wouldn't worry too much about waking her to eat. But, if she hasn't been gaining weight or her output is less than normal, keep waking her up. The only times I woke my DD to eat was when I was engorged or during the brief period that her weight was a concern. Newborns do sleep a LOT. She'll start to have longer wakeful periods soon.